The trend of new-generation electronic products is toward miniaturization and their use in high-frequency data transmission. This poses an increasingly strict requirement of the materials selected for manufacturing circuit boards, as the wirings on the circuit boards are distributed thereon at an increasingly high density. The major considerations given to electrical properties include the dielectric constant Dk and the dissipation factor Df. In general, the signal transmission speed of a laminate is inversely proportional to the square root of the dielectric constant Dk of the material from which the laminate is made, and thus the minimization of the dielectric constant Dk of the laminate material is usually advantageously important. The lower the dissipation factor Df is, the lesser the signal transmission attenuation is; hence, a material of a low dissipation factor Df provides satisfactory quality of transmission. The objective of coupling high-frequency electronic components to a circuit board is to maintain a transmission speed and ensure the integrity of the signals transmitted. The laminate of circuit board is necessary to provided with a low dielectric constant Dk and a low dissipation factor Df. Moreover, to keep electronic components operating well at a high temperature and in a high humidity environment, the circuit board must manifest such characteristics as being heat resistant, nonflammable, and of low hygroscopicity.
U.S. Pat. No. 7,989,081 (hereinafter referred to as citation 1) discloses a resin composite copper foil for use in a printed circuit board which comprises a copper foil and a resin layer which contains a polyimide block copolymer and a maleimide. The resin layer is formed on the surface of the copper foil. The polyimide block copolymer is formed from units characterized by a specific structure and a fixed range of proportions.
US2013040517 (hereinafter referred to as citation 2) discloses a resin composition for use in a printed circuit board. The resin composition comprises a polyimide resin, a thermosetting resin and a filler. The polyimide resin is formed from repeated units characterized by a specific structure and a fixed range of proportions.
Both the resin compositions disclosed in citations 1, 2 use a diamine of a specific structure, such as 1,3-bis(4-aminophenoxy)benzene (TPE-R) or 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP). The diamine reacts with an acid anhydride to form a polyimide resin. In practice, the use of the polyimide in forming a resin film or prepreg for manufacturing a circuit laminate has two drawbacks. First, the aforesaid polyimide resin does not dissolve in a toluene solvent. Second, the circuit laminate thus manufactured is characterized disadvantageously by high dielectric properties, dryness of the resultant laminate, numerous voids, and requiring a high lamination temperature.
Accordingly, it is important to develop a material of a low DK, a low DF, satisfactory heat resistance, and high adhesiveness, so as to be for use in printed circuit board manufacturing.